This project seeks to develop tumor-specific molecular probes using combinatorial ligand libraries based on small organic molecules. Human tumor tissue will be used as a target for affinity screening of peptide and trimeric N-substituted glycine (peptoid) libraries to select ligands that can distinguish carcinomas of the breast from carcinomas of the lung. The focus of this proposal on breast and lung malignancies will serve as proof-of-principle. Ultimately, the resulting technologies will be applicable to the high-througout molecular profiling of malignancies representing a wide range of differentiation lineages. The project will initially develop efficient methods for the selection of tumor-specific peptide ligands using phage display technologies. A novel partially degenerate codon strategy will be used to develop improved peptide phage display libraries containing equal representation of all twenty amino acids with no stop codons, thus permitting for the first time the complete and unbiased sampling of all possible random hexapeptides. Furthermore, efficient methods will be developed for the identification of tumor-specific trimeric peptoids from synthetic, encoded combinatorial libraries. The encoding strategy employed involves embedding an easily detectable, nonradioactive isotopic signature within each library member, enabling the straightforward decoding of much larger synthetic libraries than heretofore possible. The small molecule libraries that will be screened represent a wide range of chemical functionalities that have the potential to compose high affinity ligands for a subset of cellular target molecules distinctive for a given cell type. The selected ligands will be used to optimize protocols for histochemical discrimination of breast and lung adenocarcinoma using a range of diagnostic modalities, including paraffin-embedded tissue, frozen sections, and fine needle aspiration. In a later stage of this project, the selected ligands will be evaluated for their diagnostic capabilities in prospective studies using tissue obtained from surgical specimens.